We use reciprocal pronouns when each of two or more subjects is acting in the same way towards the other. For example, A is talking to B, and B is talking to A. So we say:
A and B are talking to each other.
The action is "reciprocated". John talks to Mary and Mary talks to John. I give you a present and you give me a present. The dog bites the cat and the cat bites the dog.
There are only two reciprocal pronouns, and they are both two words:
each other
one another
When we use these reciprocal pronouns:
there must be two or more people, things or groups involved (so we cannot use reciprocal pronouns with I, you [singular], he/she/it)
they must be doing the same thing
Look at these examples:
John and Mary love each other.
Peter and David hate each other.